Various devices are known for forming stacks of banknotes. One such device is described in published European patent application No. 0684929. This discloses an apparatus which incorporates a pusher plate with which a banknote may be pushed from the plane along which the banknote is transported to the stacking mechanism (transport plane), into a cashbox situated adjacent to the banknote plane. The pusher plate is connected by a pivoted lever arrangement via a cam, to a drive motor. The pivoted lever arrangement operates with a "scissors action" to cause the pusher plate to push the banknote into the cashbox against the action of a spring mounted stack surface. The banknotes are retained in a stack in the cashbox, when the pusher plate is withdrawn, by flanges which abut the ends of the uppermost surface of the banknote stack.
Although this type of arrangement provides an efficient method of stacking banknotes, the required depth of stroke of the pusher plate is linked to the size of the aperture through which the banknote is pushed. Thus, a short depth of stroke is only possible if the aperture is relatively large. However, cashboxes with relatively large apertures suffer from the disadvantage of being difficult to make secure (i.e. self closing) on detachment from the stacking device. The cashbox aperture may be made smaller by increasing the depth of stroke of the pusher plate. However, an increased depth of stroke results in an increased cashbox depth for any given size of banknote stack. As space is often at a premium in such circumstances, for example in combined banknote validator and stacker devices, this too is an undesirable consequence.
Furthermore, if banknotes of differing lengths are to be stacked in a cashbox incorporating stack retaining flanges, the aperture must be significantly shorter than the length of the shortest banknote to be stacked. This is in order that the flanges at the ends of the aperture may retain even the shortest banknotes. This results in a minimum length of pusher plate stroke being further increased in order to successfully stack the longest banknotes through the same aperture size and hence a corresponding increase in the depth of the cashbox.
In order that the flanges should retain the stack of banknotes, it may be important that the banknotes are presented for stacking in a predetermined orientation. For example, if a banknote of maximum length is skewed on being stacked, its greater diagonal length may prevent it from being successfully stacked. Additionally, it may also be important that the banknotes are accurately positioned lengthwise with respect to the cashbox aperture, in order to be reliably stacked. A sufficient lengthwise offset will result either in an end of the banknote not being stacked, or alternatively an end of the banknote not being retained by a flange, or both.
As cashboxes used with such devices often incorporate a spring mounted stacking surface against which a pusher plate or piston must work, a further problem may arise in such devices. Namely, despite successfully pushing the banknote into the cashbox, the banknote may not completely flatten against the stack. As the stack surface is again biased against the retaining flanges by the spring mounted stacking surface banknotes may become crumpled, causing an irregular banknote stack.
U.S. Pat. No. 4,809,967 and U.S. Pat. No. 5,014,857 disclose a stacking device of the piston type which aims to address the problem of ensuring that banknotes flatten correctly on the stack surface during the stacking process. These disclosures teach to incorporate pivotally mounted "unfolding" plates in the piston assembly. These are arranged to displace horizontally as the piston stroke increases in the vertical direction; thus assisting in flattening a banknote against the stack.
However despite assisting with flattening banknotes in the stacking procedure the device of U.S. Pat. No. 4,809,967 and U.S. Pat. No. 5,014,857 suffers from the same drawback as that of EP 0684929A, in that a short depth if stroke is only possible of the cashbox aperture is relatively large; or, conversely a small aperture is only achievable if the stroke length is relatively long.
A further stacking device is disclosed in U.S. Pat. No. 4,834,230 and U.S. Pat. No. 4,807,736 which employs a pair of rotors in place of a piston in order to stack banknotes in a cashbox. However, like the device of U.S. Pat. No. 4,809,967 and U.S. Pat. No. 5,014,857, this device suffers from the disadvantage that a short depth of stroke is only possible if the cashbox aperture is relatively large. Additionally, such a device may suffer from the disadvantage of a banknote being incorrectly stacked (for example, one end of the banknote not being retained in the cashbox by a retaining flange) if the banknote is erroneously presented for stacking in a non-central manner.
A further such device is described in granted European patent 0470329. This discloses an apparatus which transports banknotes between opposing belts entrained around rollers of a carriage, which is arranged to traverse an open surface of a cashbox. As the carriage moves over the stack of banknotes, the entrained banknote is deposited on the stack. The stack of banknotes is retained in the cashbox by one of the transporting belts which lie across the uppermost surface of the banknote stack.
Such a device does not require vertical movement of the piston or pusher, and hence the cashbox depth can be smaller for a given capacity. However, this arrangement also requires the cashbox construction to be substantially open and consequently difficult to make secure on detachment from the stacking device. Indeed in such a design the aperture of the cashbox must be at least as large as the banknotes which are to pass through it.